1. Field of the Invention
The invention relates to a nozzle plate for print heads which are used in ink jet and colored-liquid jet printers and to a method for its production. The purpose of the invention is to produce such nozzle plates and the print heads fitted therewith more economically and to improve their function in respect of printing speed and resolution.
2. Description of the Related Art
Nozzle plates for ink and colored-liquid jet print heads are known (Hewlett-Packard Journal, August 1988, pages 28 to 31) (EP-495,663; EP-500,068); such nozzle plates contain 12 to about 100 nozzles with a hole diameter of down to 20 .mu.m. Ahead of each nozzle there lies an ink chamber which communicates with an ink container via specially shaped channels. A device for ejecting droplets having a volume of 1 to 1000 picoliters communicates with each nozzle. The print head is frequently obtained by joining together the ink container with, in general, three plates, one plate being a thin-layer structure, the next plate being a lithographically produced plastic structure with a feed channel and ink chamber (channel plate), and the third plate containing the nozzles (nozzle plate). Both the production of the nozzle plate and of the channel plate and the joining together of the plates to form the print head require considerable effort and great precision.
The nozzle plate is produced, for example, by laser treatment of plastic parts. In other methods, a conductive base plate is used, which is provided at particular places with a non-conducting plastic layer. The non-conducting places are circular; their spacing corresponds to the intended spacing of the nozzles in the nozzle plate. Metal is deposited electrolytically on the base plate. This metal layer is thicker than the non-conducting layer, and the electrolytically deposited metal inevitably grows over the edge of the nonconducting places onto the non-conducting layer. In this way, smaller nozzle diameters are implemented than corresponds to the dimensions of the lithographically produced, non-conducting places of the plastic layer. In order to maintain the nozzle cross-section and its fluctuation from nozzle to nozzle within the prescribed tolerances, complex manufacturing and measuring methods have to be applied. In the latter production method described, the spacing between holes is inevitably greater than the thickness of the plate to be produced. Since the plate must have a minimum thickness for reasons of stability, the smallest spacing possible between holes and thus also the printing density are limited.
According to EP-495,663, the channel structures and the nozzle carrier are produced by casting. The nozzles are bored individually in each case by means of a laser beam. The channel structures and nozzles are produced in two steps according to completely different methods. Furthermore, finishing is required. This method is also very complex.